This application claims the benefit of priority to Japanese Patent Application No. 2004-146132, filed on May 17, 2004, herein incorporated by reference.
1. Field of the Invention
The present invention relates to a key switch and a keyboard input device using the same and, particularly, to a key switch which can go up and down while a key top is supported in a horizontal state, and a keyboard input device using the key switch.
2. Description of the Related Art
In Japanese Registered Utility Model No. 3067387, a conventional key switch is disclosed, which will now be described with reference to FIGS. 6 and 7. In the key switch, an uppermost key top 50 is formed so as to horizontally extend, like a space key and so on. At a center of a rear surface of the key top 50, a projection 53 is formed. Referring to FIG. 6, on the right side of the projection 53, a first supporting groove 51 and a second supporting groove 52 outside the first supporting groove 51 are formed.
Further, in FIG. 6, on the left side of the projection 53, a slide groove 54 is formed so as to face the first supporting groove 51 with the projection 53 interposed therebetween.
Further, a slide shaft 71a which is formed at an upper end portion of a first lever 71 is slidably engaged with the slide groove 54. A rotational shaft 72a which is formed at an upper end portion of a second lever 72 is rotatably engaged with the first supporting groove 51.
The first and second levers 71 and 72 are supported by a supporting member 73 provided substantially at their central portions to be linked together in an X shape. A rotational shaft 80a which is formed at an upper end portion of a torsion bar 80 is engaged with and supported by the second supporting groove 52. The torsion bar 80 is formed by bending a metal bar.
A slide shaft 71b which is formed at a lower end portion of the first lever 71 is slidably supported by a slide groove 61 formed on a base plate 60.
A rotational shaft 72b which is formed at a lower end portion of the second lever 72 is rotatably supported by a supporting member 62 formed on the base plate 60.
Further, outside the supporting member 62 on the base plate 60, a rotational supporting member 64 is formed so as to rotatably support a curved portion 80b formed at a lower end portion of the torsion bar 80. The rotational supporting portion 64 is provided with a hole therein through which the curved portion 80b of the torsion bar 80 is inserted.
Further, a hollow elastic member 66 is press-fitted and mounted on the projection 53 of the key top 50.
On the base plate 60, a sheet member 65 provided with a membrane switch (not shown) formed therein on a portion where the elastic member 66 is disposed is provided. In this case, if the key top 50 is pressed downward, the elastically deformed elastic member 66 presses on the sheet member 65. Then, the membrane switch is operated, such that a switch circuit is switched.
However, in the above-described conventional key switch, the key top 50 is reduced in thickness so as to reduce the thickness of the key switch. Thus, when the key top 50 is formed so as to horizontally extend, like a shift key or a space key, if a corner portion of the key top 50 in a horizontal direction is pressed, deformation such as torsion occurs in the key top 50.
In particular, when the corner portion of the key top 50 disposed at an opposite side to a portion which supports the rotational shaft 80a of the torsion bar 80 shown in FIG. 7 is pressed, deformation such as torsion is caused by a biasing force of the elastic member 66. Then, the key top 50 is inclined, which makes it difficult to perform a normal switch operation.